“Bright eyes make the heart glad.” The light of the eyes is that which someone sees that is a wonderful sight to him or her. Physiologically, this verse shows us a great deal about the working of the body. Seeing things that are a blessing and light up the eyes also makes the heart rejoice, and good news “makes fat,” or adds health and strength to a person’s bones.
“fattens the bones.” The use of “fattens” or “makes fat” here is the common use of “fat” for “healthy, prosperous.” Also, “bones” is literal, because when we feel good it affects our whole body, even our bones, but it is also a synecdoche of the part where the “bones” are the “part,” but the deeper meaning of the verse is that good news makes the whole body healthy. It would be natural for “bones” to be put for the whole body because the bones are the very foundation of the body, and if they are not healthy, the body is not healthy. [For more on bones and health, see commentary on Prov. 17:22].